Streptococcus mutans has been recognised for many years as the major organism responsible for the development of dental caries in mammals. Various vaccines have been proposed in the past based on various antigenic fragments of S. mutans. One such vaccine is described in British Patent No. 2,060,647 based upon the antigen known as I or I/II. Antigen I has a molecular weight, as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of 146-155 Kd. Antigen I/II is believed to be a conjugate of antigen I and antigen II, this I, II antigen having a molecular weight determined by SDS-PAGE of 175-195 Kd. U.S. patent application Ser. No. 579,117 now U.S. Pat. No. 4,594,244 describes antigen X which is a much smaller molecule having a molecular weight, determined by SDS-PAGE of about 3.5-4.5 Kd but which appears to include the same antigenic determinants included within antigens I and I/II.
Antibodies against antigens I, I/II and X are known. The above-mentioned British Patent describes the raising of antibodies against antigens I and I/II by conventional procedures in experimental animals, for example rhesus monkeys, rabbits and mice. These antibodies are proposed primarily for the purification of the antigen by affinity chromatography but the Patent Specification mentions the possibility of using such antibodies for passive immunisation by conventional means. Conventional passive immunisation involves parenteral administration of the antibodies but while such techniques are theoretically available, as a practical matter, passive immunisation has never been regarded as clinically attractive and indeed, the British Patent refers to the preferred use of the antigenic materials for direct immunisation.
Monoclonal antibodies against antigen I and antigen I/II are described in Smith et al, Infection and Immunity, Volume 46, No. 1, pages 168-175 (1984). This Paper describes the specificities of the various monoclonal antibodies by direct binding and inhibition with the pure streptococcal antigens with a solid phase radioassay. Conventional antisera to S. mutans serotype c, of the type described in the above-mentioned British Patent, cross-react with serotypes c, e and f (and g) while the monoclonal antibodies derived from antigen I/II of serotype c react predominantly with serotype c antigen and shows low titre reactivity with serotype f and possibly e. The slight cross-reactivity between S. mutans cells of serotype c and f could be further differentiated by absorption of any of the three monoclonal antibodies to I/II with cells of serotype c. Parallel studies of monoclonal antibodies with cells of S. mutans and their ammonium sulphate precipitated culture supernatants suggested that some antigenic determinants are retained predominantly on the cell surface but others are readily shed into culture medium so that they are detected both on the cell surface and in the culture medium. Unlike the polyclonal antibodies, the monoclonal antibodies are capable of discriminating single antigenic determinants and the Paper suggests that this can be applied to the study of the shedding of antigens from microorganisms into the environment such as the gut or gingival sulcus.